Reactive P-N-Si FR for polyester elastomer

A complex P-N monomer and a P-siloxane oligomer reacted into polyester achieved UL 94 V-0 (3mm) without dripping. The P-N monomer was synthesised from dimethyl 5-Aminoisophthalate, diphenylphosphinic chloride and the P-siloxane oligomer from dihydroxydiphenylsilane and phenylphosphonic dichloride (the chlorine not being present in the final synthesised molecules). These PIN compounds were reacted into thermoplastic polyester elastomer at a total of 30% loading, increasing LOI from 18% (neat polyester) to over 29%, reducing peak heat release rate by 15% and achieving UL 94 V-0 (3 mm, NR for neat polyester) with no burning drips. Total smoke production was however increased by over +50%. Tensile strength was considerably increased but elongation at break was halved. The fire performance is attributed to a combination of phosphorus gas phase action, phosphorus-silicon synergy enhancing char formation and silica improving char stability.

“Construction of P-N-Si multi-element synergistic flame retardant system in thermoplastic polyester elastomer towards intrinsic fire safety and anti-dripping”, Tian et al., Polymer Degradation and Stability 248 (2026) 112061 https://doi.org/10.1016/j.polymdegradstab.2026.112061